 Atrial reservoir function

Atrial reservoir function is the temporary storage of returning blood in an atrium during a phase when its inflow exceeds its outflow. For the left atrium, it is especially relevant while the mitral valve is closed during ventricular systole. It differs from passive onward passage, or atrial conduit function, and from the active late-filling contribution of atrial contraction.^[ref]

A direct volume measure is the excursion $\Delta V=V_{\max }-V_{\min }$ over a specified cardiac cycle. Its denominator matters when it is converted into a ratio. An original example with volumes 70 and 40 mL gives $\Delta V=30$ mL, but $\Delta V/V_{\min }=75\%$ and $\Delta V/V_{\max }\approx 42.9\%$. These ratios describe different normalizations of the same excursion, not contradictory measurements.

The governing storage balance isA constant net inflow of 60 mL/s for 0.4 s stores 24 mL in this idealized interval. Neither the peak inflow rate nor a single chamber volume alone supplies the required integral. Over a repeating cycle with no net accumulation, total inflow and outflow must balance even though storage changes within the cycle.

The volume excursion also does not identify how long each parcel remains in the left atrium. A primary study reconstructed atrial flow using time-resolved computed tomography and computational fluid dynamics, then followed modeled particles to distinguish conduit, reservoir and longer-residence components.^[ref] Two atria can have similar maximum and minimum volumes while differing in which blood passes directly onward or remains through later phases. Storage volume and parcel residence are related questions, but they are different measurements.